A nuclear fuel assembly for Light Water Reactor (LWR), namely Boiling Water Reactor (BWR) or Pressurized Water Reactor (PWR), conventionally comprises a bundle of longitudinally extending fuel rods parallel to each other and arranged in a lattice, a lower nozzle and an upper nozzle at the longitudinal ends of the fuel assembly and a structure for connecting the lower nozzle and the upper nozzle.
In operation, the nuclear fuel assembly is placed in a nuclear reactor core such that the fuel rods extend vertically. Coolant fluid is caused to flow at high velocity longitudinally upwardly between the fuel rods. Coolant enters the nuclear fuel assembly through the lower nozzle and exits the nuclear fuel assembly through the upper nozzle. Water is used in LWR and serves as a coolant for thermal exchanges and as a moderator for the nuclear reaction.
Small debris present in the coolant might damage the fuel rods and lead to stopping the nuclear reactor in view of changing a damaged fuel rod in a fuel assembly or changing a whole fuel assembly. However, fuel assemblies are expensive and stopping the nuclear reactor is expensive for the operator. To mitigate this risk, in a known manner, a debris filter is placed upstream the bundle of fuel rods to trap debris. Conventionally the lower nozzle of a LWR fuel assembly comprises such a debris filter.
U.S. Pat. No. 4,684,495 discloses a lower nozzle for use in LWR fuel assemblies having a lower tie plate, a skirt extending axially from the lower tie plate and defining a housing and a debris filter snap-fitted in the housing.